In U.S. Pat. No. 3,601,300, dated Aug. 24, 1971, there is disclosed a pneumatically operated nailing machine. The machine includes a hollow housing which is supplied with air under pressure. A reciprocatable blade extends through the bottom of the housing for sequentially driving nails into a workpiece. A reciprocatable differential piston unit is located in the housing. The piston has a lower, large diameter piston and an upper, small diameter piston connected by a piston rod. Means is provided for securing the reciprocatable nail driving blade to the lower end of the differential piston unit so as to advance and retract the blade as the differential piston unit is reciprocated. A cylinder sleeve is reciprocatably mounted in the housing and it has a cylinder reciprocatingly receiving the lower, large diameter piston of the differential piston unit. A cylinder member is located in the housing and it has a cylinder reciprocatingly receiving the upper, small diameter piston of the differential piston unit. The cylinder member includes passageways for venting to atmosphere an upwardly facing annular valve seat carried thereby and the cylinder thereof above the upper, small diameter piston of the differential piston unit. The housing has passageways for venting to atmosphere the cylinder of the cylinder sleeve below the lower, large diameter piston of the differential piston unit. The cylinder member also has passageways for continuously supplying air under pressure from the hollow housing to the cylinder thereof below the upper, small diameter piston of the differential piston unit. The machine of the patent further includes control valve means, which in one condition, supplies air under pressure from the housing below the cylinder sleeve for moving the cylinder sleeve upwardly to a position whereby the cylinder of the cylinder sleeve above the lower, large diameter piston of the differential piston unit is sealed from air under pressure in the housing and is vented to atmosphere. The control valve means is also operative, when in another condition, for venting to atmosphere air from below the cylinder sleeve for allowing air under pressure in the housing to move the cylinder sleeve downwardly. This causes the air under pressure in the cylinder of the cylinder sleeve above the large diameter piston of the differential unit to overcome the force of the air under pressure in the cylinder member below the upper, small diameter piston of the differential piston unit and to move the same downwardly to advance the nail driving blade.
The control valve means of the patented machine includes a first valve having a normal position and movable to a second position when the nailing machine is placed against an object into which a nail is to be driven, and a second valve having a normal position and movable to a second position when a control trigger is manually depressed. The arrangement is such that air from below the cylinder sleeve is vented to atmosphere to move the cylinder sleeve downwardly and advance the nail driving blade only when both valves are moved to their second positions.
The housing of the machine disclosed in U.S. Pat. No. 3,601,300 has a foot plate secured thereto below the cylinder sleeve and the lower, large diameter piston of the differential piston unit through which the reciprocatable nail driving blade extends. A stationary nail guide plate and blade guide plate are secured to the foot plate for guiding the reciprocatable nail driving blade and a nail to be driven thereby. The blade guide plate has a pair of channels for slidably receiving a pair of pins which, when placed against a workpiece, acts to unseat the first valve of the control valve means. A magazine is also secured to the foot plate for feeding nails to the nail guide plate. The upper end of the reciprocatable nail driving blade of the machine disclosed in said patent is T-shaped, and a special two-part separable holder is employed to secure the blade to the lower end of the differential piston unit.
The machine of the U.S. Pat. No. 3,601,300 is adapted for use with nails of one size, and while guide means is provided for the nail as it is severed and then driven into a workpiece by the blade, the nails, in certain instances, will not always enter the workpiece at the proper angle, and, as a result, another nail will have to be used. These occurrences are due, in the main, to the nail feeder device of the patented machine, and to the lack of adequate support for the nails by the nail guide means at the point of severance by the nail driving blade. In addition, while the nailing machine of the patent provides excellent nailing force with a minimum amount of compressed air, the amount of compressed air used, and, concomitantly, the amount of force generated thereby is determined by the size of the nail which can be used in the machine. A larger sized nail, of course, would require a greater force to properly embed it in a workpiece. Since the patented machine is limited to use with nails of one size, the generation of a sufficient force to accommodate nails of various sizes is not a consideration in the construction of the patented machine.